(AP) - President Barack Obama stepped into the OvalOffice for the first time as chief executive on Wednesday andsummoned economic advisers and top military officials to separatemeetings aimed at delivering the change he promised as a candidate.

A multi-denominational prayer service at Washington NationalCathedral and an open house at the presidential mansion were alsoon the schedule of the 44th president, taking office on a promiseto fix the battered economy and withdraw U.S. troops from theunpopular war in Iraq on a 16-month timetable.

The shift in administrations - former President George W. Bushwas back home in Texas - was underscored in far-off Guantanamo Bay,Cuba, where a judge granted Obama's request to suspend the warcrimes trial of a young Canadian. The judge, Army Col. PatrickParrish, issued a one-sentence order for the 120-day continuancewithout so much as a hearing, possibly the beginning of the end forthe former administration's system of trials for allegedterrorists.

Obama and first lady Michelle Obama sat in the first row forWednesday's invitation-only prayer service. Vice President JoeBiden and his wife, Jill, joined them, as did former President BillClinton and Sen. Hillary Rodham Clinton, D-N.Y., awaitingconfirmation as secretary of state later in the day.

"Grant to Barack Obama, president of the United States, and toall in authority your grace and good will. Bless them with yourheavenly gifts, give them wisdom and strength to know and to doyour will," prayed the Rev. Andy Stanley, one of numerous clericsfrom several religions to speak.

Obama's first White House meetings as president meshed withquickened efforts in Congress to add top Cabinet officials to theroster of those confirmed on Tuesday and to advance the economicstimulus measure that is a top priority of his administration.

Treasury Secretary-designate Tim Geithner, appearing before theSenate Finance Committee for a confirmation hearing, said enactmentof the new president's economic stimulus was essential. He alsosaid the Senate's decision last week to permit use of the second$350 installment of a financial industry bailout "will enable usto take the steps necessary to help get credit flowing."

He said Obama and he "share your belief that this program needsserious reform."

Geithner also apologized for his failure to pay personal taxesearlier in the decade, calling the omission a mistake. The taxeswere repaid in stages, some after an IRS audit and the rest after areview of his returns late last year by Obama's transition team.

A new poll underscored the sense of anticipation thataccompanied Obama into office.

The Associated Press-Knowledge Networks survey found that by a3-1 margin, people feel more optimistic about the country's futurenow that Obama has been inaugurated, including 30 percent ofRepublicans.

Obama and his wife arrived at the White House around 1 a.m.after attending 10 official inaugural balls.

Several hours later he walked into the most famous office inAmerica for the first time as president.

The new White House press secretary, Robert Gibbs, said in astatement that Obama spent 10 minutes alone and read a note leftfor him by Bush that was in an envelope marked "To: #44, From:#43."

He was then joined by White House chief of staff Rahm Emanueland, several minutes later, the first lady.

Wednesday's meeting with economic advisers was coming at a timewhen 11 million Americans are out of work and millions more feelthe loss of savings and face the prospect of foreclosures on theirhomes.

Last week, Congress cleared the way for use of a second, $350billion installment of financial-industry bailout money, apre-inaugural victory for Obama.

Democratic leaders hope to have the $825 billion economicstimulus measure to his desk by mid-February.

"Fortunately, we've seen Congress immediately start working onthe economic recovery package, getting that passed and puttingpeople back to work," Obama said in an ABC News interview."That's going to be the thing we'll be most focused on."

The war in Iraq that he has promised to end featured prominentlyin Obama's first day as well.

Defense Secretary Robert Gates and the chairman of the JointChiefs of Staff, Adm. Mike Mullen, were among those called in forthe meeting as the new president assumed the role of commander inchief.

Obama calls for a remaking of America The inauguration of Barack Obama